package network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    // 服务器的启动逻辑
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
            // 每次循环就是处理一个请求-响应过程
            // 1.读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            // 读到的字节数组,转成 String 方便后序的逻辑处理
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            // 2.根据请求计算响应(对于回显服务器来说,这一步啥都不用做)
            String response = process(request);
            // 3.把响应返回到客户端
            //   构造一个 DatagramPacket 作为响应对象
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);

            // 打印日志
            System.out.printf("[%s:%d] req: %s, resp: %s\n", requestPacket.getAddress().toString(),
                    requestPacket.getPort(), request, response);
        }
    }

    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}


